1. Field of the Invention
This invention relates to a method of treatment of pain by utilizing NMDA NR2B antagonists. In particular, substituted benzimidazole derivatives that are NMDA NR2B antagonists are utilized to treat pain.
Ions such as glutamate play a key role in processes related to chronic pain and pain-associated neurotoxicityxe2x80x94primarily by acting through N-methyl-D-aspartate (xe2x80x9cNMDAxe2x80x9d) receptors. Thus, inhibition of such actionxe2x80x94by employing ion channel antagonists, particularly NMDA antagonistsxe2x80x94can be beneficial in the treatment and control of pain.
Known NMDA antagonists include ketamine, dextromophan, and 3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (xe2x80x9cCPPxe2x80x9d). Although these compounds have been reported (J. D. Kristensen, et al., Pain, 51:249-253 (1992); K. Eide, et al., Pain, 61:221-228 (1995); D. J. Knox, et al., Anaesth. Intensive Care23:620-622 (1995); and M. B. Max, et al., Clin. Neurophannacol. 18:360-368 (1995)) to produce symptomatic relief in a number of neuropathies including postherpetic neuralgia, central pain from spinal cord injury, and phantom limb pain, widespread use of these compounds is precluded by their undesirable side effects. Such side effects at analgesic doses include psychotomimetic effects such as dizziness, headache, hallucinations, dysphoria, and disturbances of cognitive and motor function. Additionally, more severe hallucinations, sedation, and ataxia are produced at doses only marginally higher than analgesic doses. Thus, it would be desirable to provide novel NMDA antagonists that are absent of undesirable side effects or that produce fewer and/or milder side effects.
NMDA receptors are heteromeric assemblies of subunits, of which two major subunit families designated NR1 and NR2 have been cloned. Without being bound by theory, it is generally believed that the various functional NMDA receptors in the mammalian central nervous system (xe2x80x9cCNSxe2x80x9d) are only formed by combinations of NR1 and NR2 subunits, which respectively express glycine and glutamate recognition sites. The NR2 subunit family is in turn divided into four individual subunit types: NR2A, NR2B, NR2C, and NR2D. I. Ishii, et al., J. Biol. Chem., 268:2836-2843 (1993), A. Wenel, et al., NeuralReport, 7:45-48 (1995), and D. J. Laurie et al., Mol. Brain Res., 51:23-32 (1997) describe how the various resulting combinations produce a variety of NMDA receptors differing in physiological and pharmacological properties such as ion gating properties, magnesium sensitivity, pharmacological profile, as well as in anatomical distribution.
For example, while NR1 is found throughout the brain, NR2 subunits are differentially distributed. In particular, it is believed that the distribution map for NR2B lowers the probability of side effects while producing pain relief. For example, S. Boyce, et al., Neuropharnacology, 38:611-623(1999) describes the effect of selective NMDA NR2B antagonists on pain with reduced side-effects. Thus, it would be desirable to provide novel NMDA antagonists that target the NR2B receptor.
Phenol compounds described as NMDA antagonists are described in U.S. Pat. Nos. 5,306,723 and 5,436,255, and in International Patent Publications WO91/17156, WO92/19502, WO93/02052, WO94/29571, WO95/28057, WO96/37226, and EP 04422506. Benzyl piperidines substituted with phenols or imidazoles are described in Z.-L. Zhou, et al., J. Medicinal Chemistry, 42:2993-3000 (1999); T. F. Gregory, et al., Poster #94, 218th National Meeting American Chemical Society, New Orleans, La., Aug. 22-26, 1999. Other NMDA NR2B selective compounds are described in European Patent Publication EP 787493 and British J. Pharmacol., 123:463(1998). However, there continues to be a need for novel NMDA antagonists that target the NR2B receptor.
U.S. Pat. No. 5,714,498 (International Patent Publication WO94/21615) describes benzimidazole derivatives utilized as dopamine D4 antagonists.
The present invention relates to a method to treat pain, migraine, depression, anxiety, schizophrenia, Parkinson""s disease, or stroke, by utilizing NMDA NR2B antagonist, substituted-benzimidazole derivatives.